updated 08:16 pm EDT, Thu May 22, 2014

Documents related to a court battle between Microsoft and the Federal Bureau of Investigation (FBI) were unsealed this week by a federal court in Seattle, Washington. The court battle, which was over a 2013 National Security Letter requesting information on a Office 365 customer, resulted in a rare victory for consumers when Microsoft was able to successfully argue the letter's legal standing.

After the legal challenge was submitted by Microsoft, the FBI ended up withdrawing the letter request. The content of the letter had originally asked for information for an enterprise client of Microsoft's Office 365 service. Information on the specific nature of the entity or person(s) wasn't mentioned, as the National Security Letter isn't included in the document obtained by Ars Technica, but the FBI looking for non-specific information according to the unsealed documents. The client's name was redacted.

Even though the challenge ended up protecting customer data, there was another reason that Microsoft thought it important to fight against the FBI in this instance. Within the content of the letter was wording that barred Microsoft from disclosing that the data had been requested to anyone outside of their legal counsel. Microsoft's filing listed five separate counts as to why the letter should be set aside, among which were its legal grounds, the unreasonable nondisclosure agreement, and its violation of the First Amendment.

"In this case, the Letter included a nondisclosure provision and we moved forward to challenge it in court," said Microsoft general counsel Brad Smith on the Technet blog. "We concluded that the nondisclosure provision was unlawful and violated our Constitutional right to free expression. It did so by hindering our practice of notifying enterprise customers when we receive legal orders related to their data."